This invention relates to a turntable of a display apparatus, and particularly relates to a turntable that can be manually rotated.
A display apparatus such as an LCD (Liquid Crystal Display) television uses a turntable to adjust the orientation of a display portion. A conventional turntable includes a base on which the display portion is placed. The base is rotated by a motor via a power transmission mechanism. In order to prevent a finger or the like of a user from being caught between the display portion and its surrounding object, the power transmission from the motor to the base is disconnected under given conditions.
To be more specific, a first rotation-transmission body linked to the motor and a second rotation-transmission body for rotating the base are coaxially mounted on the same rotation shaft. The rotation of the motor is transmitted to the base due to the friction force between the first and second rotation-transmission bodies. When the external force is applied to the display portion, the first and second rotation-transmission bodies slide on each other, and the power of the motor is not transmitted to the base.
Further, in order to adjust the friction force between the first and second rotation-transmission bodies, it is proposed to provide a clutch nut that can be tightened and loosened to adjust the urging force with which the second rotation-transmission body is urged against the first rotation-transmission body. Such a turntable is disclosed in, for example, Japanese Laid-Open Patent Publication No. 2004-316794 (Page 5 and FIG. 1).
In the above described conventional turntable, the first rotation-transmission body has an insertion shaft on which the second rotation-transmission body is rotatably supported. An external thread formed on the circumference of the insertion shaft engages an internal thread formed on the clutch nut. By tightening the clutch nut on the insertion shaft, the second rotation-transmission body is sandwiched between the first rotation-transmission body and the clutch nut. By adjusting the tightening amount of the clutch nut, the urging force with which the second rotation-transmission body is urged against the first rotation-transmission body can be adjusted, so that the friction force between the first and second rotation-transmission bodies can be adjusted.
However, the first and second rotation-transmission bodies and the clutch nut are made of resin, and therefore the above described urging force is subject to the changes of shapes of the respective members with time, due to the creep deformation. Further, the changing rate of the urging force to the resilient deformation of the respective members (i.e., a spring coefficient) is large, and therefore the urging force may largely change even when the changes of shapes are small.
In order to reduce the influence of the changes of shapes of the respective members with time, it can be considered to urge the second rotation-transmission body against the first rotation-transmission body using an urging member whose spring constant changes by a small amount. However, in such a case, due to the provision of the urging member, the number of the components increases, and the turntable becomes large.
Moreover, the turntable of the above described publication has scale marks formed on the second rotation-transmission body, for facilitating the adjustment of the clutch nut. The scale marks are formed on the surface of the second rotation-transmission body on the clutch nut side, and indicate a rotation angle of the clutch nut. However, the adjustment of the clutch nut needs to be performed overcoming the above described friction force, and therefore it is not easy to adjust the clutch nut in alignment with the scale marks. Further, since the spring coefficient is large as described above, there may be the case where the urging force largely varies.
Furthermore, it is also possible to manually operate (rotate) the display portion, causing the first and second rotation-transmission bodies to slide on each other. However, if there is a variation in the urging force with which the second rotation-transmission body is urged against the first rotation-transmission body, there may be the case where the rotational resistance (friction) when the display portion is rotated is too large, or there may be the case where the rotational resistance is so small that the rotational position of the display portion is not stabilized. Therefore, it is demanded to accomplish a stable rotating operation whose variation (including change with time) is small.
Additionally, as the LCD television or the like becomes thin, it is demanded to miniaturize the turntable. In this regard, when the user manually adjusts the orientation of the display portion, the user pushes the end portion of the display portion by hand. In the display apparatus with a large-sized screen, the distance between the rotation axis of the display portion and the point of application of the force becomes longer. Therefore, in order to stabilize the rotational position of the display portion and to obtain an appropriate operational feeling, it is necessary to obtain a large rotational resistance to some extent while miniaturizing the turntable.